Lysine metabolism in the rat brain is found to proceed via the pipecolic acid pathway instead of the saccharopine pathway which is active in liver and other tissues. Lysine metabolism in the rat brain, therefore, is proposed as lysine yields delta 1-piperideine-2-carboxylate yields pipecolic acid yields piperideine. This pathway can only be demonstrated in intact animals but not in tissue slices or homogenates under various experimental conditions. Delta 1-piperideine-2-carboxylate or reductase and pipecolate decarboxylase, the two enzymes involved in the lysine metabolism in the brain, are under study to assess their physiological functions and developmental variations. Lysine intermediates will be tested for their possible inhibitory effects on the brain glycolytic enzyme systems. BIBLIOGRAPHIC REFERENCE: McCarron, R.M. and Y.F. Chang. Effect of Threonine of the Cell Wall Mucopeptide Biosynthesis in Streptococcus Mutans BHT. 75th Ann. Mtg., Amer. Soc. Microbiol., New York, N.Y., April 27, 1975. Abstract K116.